Imaging systems such as printers, fax machines, and copiers are virtually omnipresent, and can be found in homes and offices worldwide. The development of such systems has facilitated improvements in communications that have in turn fostered profound changes in the ways that people live and work. Telecommuting, “virtual” offices, and intra-office networks represent but a few examples of the advancements that have been made possible by modern imaging systems.
Imaging systems using electrostatic printing have found wide acceptance. In electrostatic printing, toner stored in a hopper is deposited on a media sheet, then heat-fused to the media sheet. Within the hopper are stirrers to maintain the toner in particulate form by preventing coalescing, or “clumping”, of the toner. Stirrers also serve to transfer toner towards the developer drum, and create a dusting of toner to assist the developer roller in attracting toner particles to the developer roller surface.
One example of hopper stirrer arrangements is set forth in U.S. Pat. No. 5,854,961 to Hoberock, which is directed to a toner delivery and metering apparatus including a generally U-shaped or trough member which is operative to receive toner material. The dry, non-magnetic toner particles are agitated and stirred with an oscillating or rotating stirrer blade and passed between the sidewalls of a toner supply rod. The toner supply rod is rotatably mounted in the bottom of the trough member, and is operative to pass the toner particles onto the surface of the applicator and charging roller by a controlled oscillatory and agitating motion at the lower opening within the trough member.
Typical color toner particles are comprised of EP-enhancing particulates bonded to the surface of colorized polymers. Since mechanical stirrers contact particles that remain in the hopper as well as those that are transferred, particles within the hopper can be subjected to repeated and unnecessary contact with the stirrer elements. The particulate/polymer bonds can become damaged by contact with the mechanical stirrers, thus causing the toner to act inconsistently with the EP process. This inconsistency degrades print quality, and shortens the life of the cartridge/toner.
In an attempt to reduce stirrer/particulate contact, hoppers have been developed in which a primary stirrer in contact with most of the toner is used infrequently, while a smaller, secondary stirrer operates constantly in a conventional manner.
While known “two-level” stirring reduces particulate damage somewhat, such arrangements still cause unnecessary particulate damage due to constant stirrer/particulate contact. It can be seen from the foregoing that the need exists for a simple, inexpensive, arrangement for minimizing particulate damage in toner hoppers.